The book "One Witness" by Aggie Hurst and Doug Brendel. A missionary David Flood and his wife go to Africa, where they give birth to their daughter and then the wife dies. David is forced to abandon his daughter and becomes angry with God for 40 years, being now without his wife and daughter while making only one convert, a young boy. But that boy went on to win hundreds for Christ. And the daughter, upon learning of this, found her father who she hadn't seen in 40 years, and wins him back to the Lord shortly before he passes.